Vacuum tube



7 1,626,858 May 1927- H. E. METCALF VACUUM 'I UBE Filed Feb. 28. 1924,[170 entor Patented May 3, 1927.

UNITED STATES PATENT OFFICE.

HERBERT'E. ME'I'CALF, OF SAN LEANDRO, CALIFORNIA, ASSIGNOR TO THEMAGNAVOX COMPANY, OF OAKLAND, CALIFORNIA, A CORPORATION OF ARIZONA.

? vacuum TUBE.

, Application filed February 28, 1924. Serial No. 695,681.

This invention relates to vacuum tubes of the three-electrode type, foruse as rectifiers, amplifiers and electric-wave generators.

The object of the invention is to improve the construction and operationof such a device, whereby it is made more sensitive to weak oscillationsandwhereby the internal capacity of the device is kept to a minimum.especially the capacity between the grid anil plate.

n the construction of three electrodc tubes, the practice has becomequite general toemploy a-gridbetween the plate and filament.' whichoffers mechanical obstruction and interferes with the sensitivity of thedevices In' the present invention I place the grid out of'theelectron-stream, yet in such a position and of such construction thatits minutest voltage changes fully effect the emission of electrons fromthe filament, whereby extreme sensitiveness is obtained.

In the accompanying drawings I show a variety of difierent forms whichmy invention may assume.

In the drawings,

Fig. 1 shows aside view in perspective of a tube embodying my invention;

Fig. 2 shows an end view of the same;

Fig. 3 shows a side elevation of a tube using a slightly difi'erent formof grid;

Fig. 4 shows a cross-section of the form of device illustrated in Fig.3;

Fig. 5 shows a side elevation of a further modification of theinvention; I

Fig. 6 shows a similar view of another form of the invention;

Fig. 7 shows a cross-section of the form of device illustrated in Fig.6;

Fig. 8 shows a diagram illustrating the current and phantom circuits ofthe tube;

\ Fig. 9 shows a dia ram illustrating the action of electro-staticfields within the tu e.

Fig. 10 is a view in diagram showing a' modificationof the presentinvention when a plurality of grid members are utilized with a singleplate. i Fig. 11 is a view in diagram showing the modification of theinvention when a plurality of grid members and a plurality of platemembers are used in connection with a single filament.

follows exactly the course of the filament and is disposed with its edgetowards the fila.ment..so that the maximum action of the grid voltage isobtained without mechanical obstruction of the electron flow. In Fig. 1the grid consists simply of a straight strip of metal, whereas in Fig. 3the grid is made in the form of a V-shaped strip of metal, to conformwith a filament of a similar configuration. Various other shapes anddesigns of grids may be employed, depending on the shape of thefilament. In Fig. 5 I show the grid as consisting of a wire whichfollows substantially the course of the filament, and so positioned asto concentrate the grid voltage on the filament by narrowing down theelectro-static field of the grid and focusing the same on to thefilament. As illustrated in Fig. 6. the grid may be molded so as topresent a rib or projection C close to the filament and so as toconcentrate its field on the filament.

Inasmuch as the usual vacuum tube circuit consists of two separatecircuits. both bound together, there is a phantom capacity between thegrid and filament as indicated at D in Fi 8. between the grid and plateas indicate at E, and between the filament and plate as indicated at F.I find that the sensitivity of the tube will be increased by thearrangement herein shown. inasmuch as the electro-static field betweenthe plate and grid converges or focuses on the thin edge of the grid.This field is illustrated in diagram in Fig. 9. The filament being justinside this focus and in longitudinal alignment therewith,is fully actedupon by slight changes in such electro-static field. In addidisposed asto place the filament justwithin the focus of the electro-static fieldbetween the grid and plate, and with the said grid concentrating theelcctro-static filament-grid field on the filament, affords everydesired objectin a three-electrode tube construction without obstructionof the passage of electrons between .the filament and the plate.

It is preferred to cover the plate with a thin film of volatile metalsuch as mercury, sodium, potassium, etc. It is well known that metallicvapors tend to increase the sensitiveness of the tubes and also increasethe vacuum, due to their occlusive properties. By covering the platewith a thin film of these metals I find that great sensitivity isobtained. This may be done by placing the volatile metal on the filamentand heating the latter. or by placing it upon the grid and heatingbycathode rays, whereby it is thrown off from the grid and is depositedupon the plate, leaving the grid clean. There are other ways well knownin the art for depositing a volatile metal upon the plate. Other formsof construction than those here illustrated and described will be appar--entto those skilled in the art, and may be employed without departingfrom the spirit of my invention as disclosed in the appended claims.

\Vhat I claim and desire to secure by Letters Patent is:

l. A three-electrode tube having a plate on one side of the filament anda linear grid on the. opposite side, in the form of a thin strip withits edge close to and following substantially the course of the filamentand disposed towards the plate.

2. A tln-ee-electrode tube having a plate, a lilan'ient. and a grid, thelatter in the form of a strip having an edge surface followingsubstantially the course of the filament, said grid being locatedoutside of the electron path between the plate and filament and being soarranged with respect to the plate and filament as to concentrate theelectrostatic field between the grid and plate upon the filament.

3. A three-electrode tube having a curved plate, a filament and a grid,the latter composed of a plurality of narrow strips, each followingsubstantially the course of the filament, all of said grid members beinglocated outside of the electron path between the plate and filament anddisposed radially with respect to the plate.

4. A three-electrode tube comprising an anode ('Oll'lPOSd of a pluralityof curved plates and a grid also composed of a plurality of narrowstrips, each following substantially the course of the filament, all ofsa d grid members being located outside of the electron path between theanode and filament and disposed radially with respect to the anodeplates. 7

HERBERT E. METCALF.

